1. Field of the Invention
This invention relates to ballistic resistant articles having excellent resistance to deterioration due to liquid exposure. More particularly, the invention pertains to ballistic resistant structures and articles formed from a hybrid of woven and non-woven fibrous components that retain their superior ballistic resistance performance after exposure to liquids such as sea water and organic solvents, such as gasoline and other petroleum-based products.
2. Description of the Related Art
Ballistic resistant articles containing high strength fibers that have excellent properties against projectiles are well known. Articles such as bulletproof vests, helmets, vehicle panels and structural members of military equipment are typically made from fabrics comprising high strength fibers. High strength fibers conventionally used include polyethylene fibers, aramid fibers such as poly(phenylenediamine terephthalamide), graphite fibers, nylon fibers, glass fibers and the like. For many applications, such as vests or parts of vests, the fibers may be used in a woven or knitted fabric. For other applications, the fibers may be encapsulated or embedded in a matrix material to form non-woven rigid or flexible fabrics.
Various ballistic resistant constructions are known that are useful for the formation of hard or soft armor articles such as helmets, panels and vests. For example, U.S. Pat. Nos. 4,403,012, 4,457,985, 4,613,535, 4,623,574, 4,650,710, 4,737,402, 4,748,064, 5,552,208, 5,587,230, 6,642,159, 6,841,492, 6,846,758, all of which are incorporated herein by reference, describe ballistic resistant composites which include high strength fibers made from materials such as extended chain ultra-high molecular weight polyethylene. These composites display varying degrees of resistance to penetration by high speed impact from projectiles such as bullets, shells, shrapnel and the like.
For example, U.S. Pat. Nos. 4,623,574 and 4,748,064 disclose simple composite structures comprising high strength fibers embedded in an elastomeric matrix. U.S. Pat. No. 4,650,710 discloses a flexible article of manufacture comprising a plurality of flexible layers comprised of high strength, extended chain polyolefin (ECP) fibers. The fibers of the network are coated with a low modulus elastomeric material. U.S. Pat. Nos. 5,552,208 and 5,587,230 disclose an article and method for making an article comprising at least one network of high strength fibers and a matrix composition that includes a vinyl ester and diallyl phthalate. U.S. Pat. No. 6,642,159 discloses an impact resistant rigid composite having a plurality of fibrous layers which comprise a network of filaments disposed in a matrix, with elastomeric layers there between. The composite is bonded to a hard plate to increase protection against armor piercing projectiles.
Hard or rigid body armor provides good ballistic resistance, but can be very stiff and bulky. Accordingly, body armor garments, such as ballistic resistant vests, are preferably formed from flexible or soft armor materials. However, while such flexible or soft materials exhibit excellent ballistic resistance properties, they also generally exhibit poor resistance to liquids, including seawater and organic solvents, such as gasoline and other solvents derived from petroleum. This is problematic because the ballistic resistance performance of such materials is generally known to deteriorate when exposed to or submerged in liquids. Accordingly, there is a need in the art for soft, flexible ballistic resistant materials that perform at acceptable standards after being contacted with or submerged in a variety of liquids, such as gasoline, gun lube, petroleum and water. The invention provides a hybrid combination of woven and non-woven ballistic resistant materials, at least one of which is formed with a matrix material that is resistant to both water and one or more organic solvents.
Hybrid ballistic resistant structures, in and of themselves, are known. For example, U.S. Pat. Nos. 5,179,244 and 5,180,880 teach soft or hard body armor utilizing a plurality of plies made from dissimilar ballistic materials, joining aramid and non-aramid fiber plies into a combined structure and utilizing polymeric matrix materials that deteriorate when exposed to liquids. U.S. Pat. No. 5,926,842 also describes hybridized ballistic resistant structures utilizing polymeric matrix materials that deteriorate when exposed to liquids. Further, U.S. Pat. No. 6,119,575 teaches a hybrid structure containing a first section of aromatic fibers, a second section of a woven plastic and a third section of polyolefin fibers.
The present invention provides an improved hybrid structure that incorporates the benefits of dissimilar materials and offers the desired protection from liquids. Particularly, the invention provides hybrid ballistic resistant structures incorporating at least one layer which is preferably formed with a hydrolytically stable, polar matrix material. Polar polymers are generally resistant to dissolution by non-polar organic solvents, and hydrolytically stable polymers are generally resistant to degradation due to sea water exposure. It has been discovered that matrix polymers having both properties advantageously contribute to the retention of the ballistic resistance properties of a fabric after prolonged exposure to potentially harmful liquids.